Fifteen- and 27-year follow-up studies of patients with borderline personality disorder show that most of them no longer meet full criteria for the disorder by age 40, and that even more show improvement by age 50. The mechanisms behind remission could include maturation, social learning, and the avoidance of conflictual intimacy. Affective instability is slower to change than impulsivity. Suicide rates in patients with this disorder are close to 10%, with most completions occurring late in the course of illness; early mortality from all causes exceeds 18%. All of these findings have clinical implications. Although treatment effects must be assessed in the context of naturalistic improvement, therapy can hasten remission.